Method and system for deposition tuning in an epitaxial film growth apparatus

ABSTRACT

A method of calculating a process parameter for a deposition of an epitaxial layer on a substrate. The method includes the steps of measuring an effect of the process parameter on a thickness of the epitaxial layer to determine a gain curve for the process parameter, and calculating, using the gain curve, a value for the process parameter to achieve a target thickness of the epitaxial layer. The value is calculated to minimize deviations from the target thickness in the layer. Also, a substrate processing system comprising that includes a processor to calculate a value for the process parameter to achieve a substantially uniform epitaxial layer of a target thickness on the substrate, where the value is calculated using a gain curve derived from measurements of layer uniformity as a function of the value of the process parameter.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/178,973, entitled “METHOD AND SYSTEM FOR DEPOSITION TUNING IN ANEPITAXIAL FILM GROWTH APPARATUS,” filed Jul. 11, 2005, the entiredisclosure of which is incorporated herein by reference for allpurposes.

BACKGROUND OF THE INVENTION

Modern processes for manufacturing semiconductor devices require preciseadjustment of many process parameters to achieve high levels of deviceperformance, product yield, and overall product quality. For processesthat include the formation of semiconductive layers on substrates withepitaxial film growth, numerous process parameters have to be carefullycontrolled, including the substrate temperature, the pressures and flowrates precursor materials, the formation time, and the distribution ofpower among the heating elements surrounding the substrate, among otherprocess parameters.

Current trends in CMOS technology are favoring processes that canproduce increasingly thin layers (e.g., dielectric layers only 60-80 Åthick or less), and films with increasing complexity. For example,conventional BiCMOS devices, using single-element silicon (Si) films,are being displaced by two-element, silicon-germanium (SiGe) films thathave superior qualities in logic and DRAM devices. As the sizes of thesedevices continue to shrink, the uniformity of the film thickness andcomposition across the substrate becomes increasingly important.Maintaining a high level of uniformity is made even more challenging dueto the increasing sizes of the substrates, with the standard substratewafer diameter moving from 200 mm to 300 mm, and beyond.

In many conventional semiconductor manufacturing process, includingepitaxial film growth processes (“EPI processes”), process parameterscan be manually adjusted to make films with the requisite uniformity offilm thickness and composition. In EPI processes for making alloy films(e.g., SiGe films), especially doped alloy films, the sensitivity ofseveral process parameters on film quality is increased, making it moredifficult to tune these parameters by hand. The increased sensitivitymakes manual control of semiconductor film growth processes much moredifficult, if not impossible.

There is also increasing complexity in the relationship between processparameters and the qualities of the manufactured film layer.Increasingly, the interdependencies of multiple process parameters on aproperty of the layer make it more difficult to find optimum values forthe parameters to achieve a target value for the property. For example,in an EPI process trying to achieve a target thickness uniformity of afilm layer across the substrate, the interdependencies of the powerratios between inner/outer and upper/lower substrate heating elementshave to be understood. Only with this understanding can the processoperator set the parameters to values that result in a sufficientlyuniform thickness of the deposited layer. Moreover, the interdependenceof the parameters make determining the parameter values much moredifficult than if the effects of each parameter on thickness uniformitywere completely independent.

Thus, there is a need for systems and methods of tuning processparameters in semiconductor film growth processes that reduce oreliminate the manual adjustment of the process parameters. There is alsoa need for systems and methods to determine values of interdependentprocess parameters for making a film layer with the desired properties.These and other needs for semiconductor film making systems andprocesses are addressed by the present invention.

BRIEF SUMMARY OF THE INVENTION

Embodiments of the invention include a method of calculating a processparameter for a deposition of an epitaxial layer on a substrate. Themethod includes the steps of measuring an effect of the processparameter on a thickness of the epitaxial layer to determine a gaincurve for the process parameter, and calculating, using the gain curve,a value for the process parameter to achieve a target thickness of theepitaxial layer. The value is calculated to minimize deviations from thetarget thickness in the layer.

Embodiments of the invention also include a method of calculatingprocess parameters for a deposition of an epitaxial layer. The methodincludes the steps of determining a first gain equation comprising afirst relationship between a first process parameter and a thickness ofthe epitaxial layer, and determining a second gain equation comprising asecond relationship between a second process parameter and the thicknessof the epitaxial layer. The method also includes calculating, using thefirst and second gain equations, values for the first and second processparameters to achieve the target thickness. The values are calculated togive a uniform distribution of a component of the epitaxial layer.

Embodiments of the invention further relate to a substrate processingsystem. The system may include a chamber, a substrate holder, locatedwithin the chamber, to hold a substrate, a precursor delivery system tointroduce one or more precursors into the chamber, a heating system toheat the substrate, and a controller to control a process parameter inthe precursor delivery system or the heating system. The system may alsoinclude a processor to calculate a value for the process parameter toachieve a substantially uniform epitaxial layer of a target thickness onthe substrate. The value is calculated using a gain curve derived frommeasurements of layer uniformity as a function of the value of theprocess parameter.

Another embodiment of the invention relates to a system to calculate aprocess parameter for a deposition of an epitaxial layer on a substrate.The system may include a processor arranged to obtain a value for theprocess parameter to achieve a target thickness of the epitaxial layer.The value for the process parameter may be obtained by measuring aneffect of the process parameter on a thickness of the epitaxial layer todetermine a gain curve for the process parameter, and calculating, usingthe gain curve, a value for the process parameter to achieve a targetthickness of the epitaxial layer. The value for the process parametermay be calculated to minimize deviations from the target thickness inthe layer.

Additional embodiments of the invention include methods of setting aprocess parameter for a deposition of an epitaxial layer on a substrate.The methods include measuring an effect of a process parameter on aconcentration distribution of a material in the epitaxial layer todetermine an effect profile for the process parameter, and calculating,using the effect profile, a value for the process parameter to achieve atarget concentration profile of the material in the epitaxial layer. Thevalue of the process parameter is calculated to minimize deviations fromthe target concentration profile in the layer.

Additional embodiments and features are set forth in part in thedescription that follows, and in part will become apparent to thoseskilled in the art upon examination of the specification or may belearned by the practice of the invention. The features and advantages ofthe invention may be realized and attained by means of theinstrumentalities, combinations, and methods described in thespecification.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a flowchart showing methods of determining a processparameter for the formation of an epitaxial film layer according toembodiments of the invention;

FIG. 1B is a flowchart showing methods of determining a first and secondprocess parameter for formation of an epitaxial film layer according toembodiments of the invention;

FIG. 1C is a flowchart showing methods of setting a process parameterfor the formation of an epitaxial film layer according to additionalembodiments of the invention;

FIGS. 2A-B shows aspects of a substrate processing system according toembodiments of the invention;

FIGS. 3A-B show film layer thickness profiles across substrate wafersafter varying two interdependent process parameters; and

FIG. 4 shows the thickness uniformity results from tuning the processparameters; and

FIG. 5 shows the thickness uniformity results from tuning the processparameters with the aid of the Epi process tuning tool.

DETAILED DESCRIPTION OF THE INVENTION

Methods and systems are described for tuning parameters in an epitaxialfilm growth process in order to achieve films with a desired thicknessuniformity and/or compositional distribution. Tunable process parametersinclude power settings for heating elements in the various substrateheating zones of the process chamber, and partial pressures and flowrate settings of the process gases used in the chamber, among otherparameters.

The methods include the creation of gain curves and/or algorithms thatmodel the effects of the process parameters on the characteristics ofthe films. For example, a gain curve may be determined that plots aratio of the power delivered to heating elements in different substrateheating zones (i.e., the process parameter) against variations in thethickness of the film layer. The gain curve may be used to calculate apower ratio that forms a film layer with minimized variations from atarget thickness. Additional aspects of embodiments of the methods willnow be described.

Exemplary Methods

FIG. 1A shows a flowchart that outlines steps in a method of calculatinga process parameter in an epitaxial growth process according toembodiments of the invention. The method includes steps to determine again curve for a process parameter. This may include setting the processparameter to a particular value 102, and measuring a property ofinterest of the film formed with that value for the process parameter104. The process parameter is then adjusted 106, and the property ofinterest is measured on a new film that is formed with the adjustedvalue of the process parameter 108. A gain curve may be determined 110,which plots the film property as a function of the value of the processparameter. Additional measurements of the property may be taken afterfurther adjustments of the process parameter to better resolve the gaincurve. For example, measurements of a film property, such as thicknessuniformity, may be plotted according to a plurality of incrementalchanges in a process parameter, such as the power ratio of two substrateheating zones, to determine the gain curve.

An accurate gain curve permits the tuning of process parameters toachieve an epitaxial growth film with target properties without furtherexperimentation. Thus, the method may include providing a target valuefor a property of the film 112, and using the gain curve to calculate aprocess parameter value for achieving the target value 114. The targetproperty may be provided to a computer programmed with the gain curve,and capable of calculating the process parameter value based on thetarget value. Alternatively, an EPI process operator may manuallydetermine the target value from a plot of the gain curve. In morecomplex models, multiple gain curves may be provided to a computer thatis operable to output values for a plurality of process parameters basedon one or more desired target values for film properties.

For example, the flowchart shown in FIG. 1B has steps for determining atwo-variable gain curve. Embodiments of the method may include settingof a first and second process parameter 120, 122. A property of theresulting epitaxial film layer is measured for these values of theprocess parameter 124, 126. Then, both the first and second processparameters may be adjusted 128, 130, and the property of the film layermeasured again with the new process parameter settings 132, 134. Atwo-parameter gain curve may be determined 136, which plots the filmproperty as a function of both process parameters. The steps ofadjusting the process parameters and measuring the effects on the filmproperty may be repeated multiple times to enhance the resolution of thegain curve.

The two-parameter gain curve permits the tuning of the processparameters to achieve an epitaxial growth film with a target value ofthe property without further experimentation. Thus, the method mayinclude providing a target value for a property of the film 138, andusing the gain curve to calculate first and second process parametervalues for achieving the target value 140. Embodiments with even morecomplex algorithms and/or gain curves that are dependent on three ormore process parameters are also contemplated.

Referring now to FIG. 1C, a flowchart is shown for methods of setting aprocess parameter for the formation of an epitaxial film layer accordingto additional embodiments of the invention. The methods include steps todetermine effect profiles that relate the values of one or more processparameters on a concentration distribution profile of a material in theepitaxial layer. The steps may include setting the process parameter toa particular value 160, and measuring the concentration distribution ofthe material in the epitaxial layer for that value for the processparameter 162. The process parameter is then adjusted 164, and theconcentration distribution measured on a new film that is formed withthe adjusted value of the process parameter 166. After incrementallyadjusting the value of the process parameter a number of times (e.g.,increasing the value of the parameter by 5% increments) an effectprofile may be determined 168, which plots the concentrationdistribution as a function of the value of the process parameter.Additional measurements of the property may be taken after furtheradjustments of the process parameter to better resolve the effectprofile (e.g. measuring changes in the concentration distribution for 1%increments in the value of the process parameter).

An accurate effect profile permits the tuning of process parameter toachieve a target concentration profile of a material in the epitaxiallayer without further experimentation. Thus in this embodiment, themethods include providing a target concentration profile 170 of amaterial, such as boron, phosphorus, arsenic, germanium, indium,gallium, tin, carbon, nitrogen, oxygen, etc., and using the effectprofile to calculate a process parameter value for achieving the targetprofile 172. The target concentration profile may be provided to acomputer programmed with the effect profile, and capable of calculatingone or more process parameter values based on the target profile.Alternatively, an EPI process operator may manually determine targetvalues from a plot of the effect profile. In more complex models,multiple effect profiles may be provided to a computer that is operableto output values for a plurality of process parameters based on thetarget concentration profiles for one or more materials.

Exemplary Systems

FIGS. 2A-B shows an example of a substrate processing system accordingto embodiments of the invention. The processing apparatus 210 shown inFIG. 2A is a deposition reactor and comprises a deposition chamber 212having an upper dome 214, a lower dome 216 and a sidewall 218 betweenthe upper and lower domes 214 and 216. Cooling fluid (not shown) may becirculated through sidewall 218 to cool o-rings used to seal domes 214and 216 against sidewall 218. An upper liner 282 and a lower liner 284are mounted against the inside surface of sidewall 218. The upper andlower domes 214 and 216 are made of a transparent material to allowheating light to pass through into the deposition chamber 212.

Within the chamber 212 is a flat, circular susceptor 220 for supportinga wafer in a horizontal position. The susceptor 220 extends transverselyacross the chamber 212 at the sidewall 218 to divide the chamber 212into an upper portion 222 above the susceptor 220 and a lower portion224 below the susceptor 220. The susceptor 220 is mounted on a shaft 226which extends perpendicularly downward from the center of the bottom ofthe susceptor 220. The shaft 226 is connected to a motor (not shown)which rotates shaft 226 and thereby rotates the susceptor 220. Anannular preheat ring 228 is connected at its outer periphery to theinside periphery of lower liner 284 and extends around the susceptor220. The pre-heat ring 228 is in the same plane as the susceptor 220with the inner edge of the pre-heat ring 228 separated by a gap 402Afrom the outer edge of the susceptor 220.

An inlet manifold 230 is positioned in the side of chamber 212 and isadapted to admit gas from a source of gas or gases, such as tank 141,into the chamber 212. An outlet port 232 is positioned in the side ofchamber 212 diagonally opposite the inlet manifold and is adapted toexhaust gases from the deposition chamber 212.

A plurality of high intensity lamps 234 are mounted around the chamber212 and direct their light through the upper and lower domes 214 and 216onto the susceptor 220 (and preheat ring 228) to heat the susceptor 220(and preheat ring 228). Susceptor 220 and preheat ring 228 are made of amaterial, such as silicon carbide, coated graphite which is opaque tothe radiation emitted from lamps 234 so that they can be heated byradiation from lamps 234. The upper and lower domes 214 and 216 are madeof a material which is transparent to the light from the lamps 234, suchas clear quartz. The upper and lower domes 214 and 216 are generallymade of quartz because quartz is transparent to light of both visibleand IR frequencies; it exhibits a relatively high structural strength;and it is chemically stable in the process environment of the depositionchamber 212. Although lamps are the preferred means for heating wafersin deposition chamber 220, other methods may be used such as resistanceheaters and RF inductive heaters. An infrared temperature sensor 236such as a pyrometer is mounted below the lower dome 216 and faces thebottom surface of the susceptor 220 through the lower dome 216. Thetemperature sensor 236, is used to monitor the temperature of thesusceptor 220 by receiving infra-red radiation emitted from thesusceptor 220 when the susceptor 220 is heated. A temperature sensor 237for measuring the temperature of a wafer may also be included ifdesired.

An upper clamping ring 248 extends around the periphery of the outersurface of the upper dome 214. A lower clamping ring 250 extends aroundthe periphery of the outer surface of the lower dome 216. The upper andlower clamping rings 248 and 250 are secured together so as to clamp theupper and lower domes 214 and 216 to the side wall 218.

Reactor 210 includes a gas inlet manifold 230 for feeding process gasinto chamber 212. Gas inlet manifold 230 includes a connector cap 238, abaffle 274, an insert plate 279 positioned within sidewall 218, and apassage 260 formed between upper liner 282 and lower liner 284. Passage260 is connected to the upper portion 222 of chamber 212. Process gasfrom gas cap 238 passes through baffle 274, insert plate 279 and passage260 and into the upper portion 222 of chamber 212.

Reactor 210 also includes an independent inert gas inlet 262 for feedingan inert purge gas, such as but not limited to, hydrogen (H₂) andnitrogen (N₂), into the lower portion 224 of deposition chamber 212. Asshown in FIG. 2A, inert purge gas inlet 262 can be integrated into gasinlet manifold 230, if desired, as long as a physically separate anddistinct passage 260 through baffle 274, insert plate 279, and lowerliner 284 is provided for the inert gas, so that the inert purge gas canbe controlled and directed independent of the process gas. Inert purgegas inlet 262 need not necessarily be integrated or positioned alongwith gas inlet manifold 230, and can for example be positioned onreactor 210 at an angle of 90° from deposition gas inlet manifold 230.

Reactor 210 also includes a gas outlet 232. The gas outlet 232 includesan exhaust passage 290 which extends from the upper chamber portion 222to the outside diameter of sidewall 218. Exhaust passage 290 includes anupper passage 292 formed between upper liner 282 and lower liner 284 andwhich extends between the upper chamber portion 222 and the innerdiameter of sidewall 218. Additionally, exhaust passage 290 includes anexhaust channel 294 formed within insert plate 279 positioned withinsidewall 218. A vacuum source, such as a pump (not shown) for creatinglow or reduced pressure in chamber 212 is coupled to exhaust channel 294on the exterior of sidewall 218 by an outlet pipe 233. Thus, process gasfed into the upper chamber portion 222 is exhausted through the upperpassage 292, through exhaust channel 294 and into outlet pipe 233.

The single wafer reactor shown in FIG. 2A is a “cold wall” reactor. Thatis, sidewall 218 and upper and lower liners 282 and 284, respectively,are at a substantially lower temperature than preheat ring 228 andsusceptor 220 (and a wafer placed thereon) during processing. Forexample, in a process to deposit an epitaxial silicon film on a wafer,the susceptor and wafer are heated to a temperature of between 550-1200°C., while the sidewall (and liners) are at a temperature of about400-600° C. The sidewall and liners are at a cooler temperature becausethey do not receive direct irradiation from lamps 234 due to reflectors235, and because cooling fluid is circulated through sidewall 218.

Gas outlet 232 also includes a vent 296 which extends from the lowerchamber portion 224 through lower liner 284 to exhaust passage 290. Vent296 preferably intersects the upper passage 292 of exhaust passage 290as shown in FIG. 2A. Inert purge gas is exhausted from the lower chamberportion 224 through vent 296, through a portion of upper chamber passage292, through exhaust channel 294, and into outlet pipe 233. Vent 296allows for the direct exhausting of purge gas from the lower chamberportion to exhaust passage 290.

According to the present invention, process gas or gases 298 are fedinto the upper chamber portion 222 from gas inlet manifold 230. Aprocess gas, according to the present invention, is defined as a gas orgas mixture which acts to remove, treat, or deposit a film on a wafer ora substrate placed in chamber 212. According to the present invention, aprocess gas comprising HCl and an inert gas, such as H₂, is used totreat a silicon surface by removing and smoothing the silicon surface.In an embodiment of the present invention a process gas is used todeposit a silicon epitaxial layer on a silicon surface of a wafer placedon susceptor 220 after the silicon surface has been treated. Process gas298 generally includes a silicon source, such as but not limited to,monosilane, trichlorosilane, dichlorosilane, and tetrachlorosilane,methyl-silane, and a dopant gas source, such as but not limited tophosphine, diborane, germaine, and arsine, among others, as well asother process gases such as oxygen, methane, ammonia, etc. A carriergas, such as H₂, is generally included in the deposition gas stream. Fora process chamber with a volume of approximately 5 liters, a depositionprocess gas stream between 35-75 SLM (including carrier gas) istypically fed into the upper chamber portion 222 to deposit a layer ofsilicon on a wafer. The flow of process gas 298 is essentially a laminarflow from inlet passage 260, across preheat ring 228, across susceptor220 (and wafer), across the opposite side of preheat ring 228, and outexhaust passage 290. The process gas is heated to a deposition orprocess temperature by preheat ring 228, susceptor 220, and the waferbeing processed. In a process to deposit an epitaxial silicon layer on awafer, the susceptor and preheat ring are heated to a temperature ofbetween 800° C.-1200° C. A silicon epitaxial film can be formed attemperatures as low as 550° C. with silane by using a reduced depositionpressure.

Additionally, while process gas is fed into the upper chamber portion,an inert purge gas or gases 299 are fed independently into the lowerchamber portion 224. An inert purge gas is defined as a gas which issubstantially unreactive at process temperatures with chamber featuresand wafers placed in deposition chamber 212. The inert purge gas isheated by preheat ring 228 and susceptor 220 to essentially the sametemperature as the process gas while in chamber 212. Inert purge gas 299is fed into the lower chamber portion 224 at a rate which develops apositive pressure within lower chamber portion 224 with respect to theprocess gas pressure in the upper chamber portion 222. Process gas 298is therefore prevented from seeping down through gap 402A and into thelower chamber portion 224, and depositing on the backside of susceptor220.

FIG. 2B shows a portion of the gas inlet manifold 230 which supplies gasto the upper zone of the processing chamber. In FIG. 2B the insert plateis shown to be constituted by an inner zone 128 and an outer zone 130.According to this embodiment of the invention the composition of theprocess gas which flows into inner zone 128 can be controlledindependently of the composition of the gas which flows into outer zone130. In addition, the flow rate of the gas to either of the two halves128 a-128 b of the inner zone 128 can be further controlledindependently from one another. This provides two degrees of control forthe gas flow for the purposes of controlling the composition of theprocess gas mix over different zones of the semiconductor wafer.

Processing apparatus 210 shown in FIG. 2A includes a system controller150 which controls various operations of apparatus 210 such ascontrolling gas flows, substrate temperature, and chamber pressure. Inan embodiment of the present invention the system controller 150includes a hard disk drive (memory 152), a floppy disk drive and aprocessor 154. The processor contains a single board computer (SBC),analog and digital input/output boards, interface boards and steppermotor controller board. Various parts of processing apparatus 210conform to the Versa Modular Europeans (VME) standard which definesboard, card cage, and connector dimensions and types. The VME standardalso defines the bus structure having a 16-bit data bus and 24-bitaddress bus.

System controller 150 controls all of the activities of the apparatus210. The system controller executes system control software, which is acomputer program stored in a computer-readable medium such as a memory152. Preferably, memory 152 is a hard disk drive, but memory 152 mayalso be other kinds of memory. The computer program includes sets ofinstructions that dictate the timing, mixture of gases, chamberpressure, chamber temperature, lamp power levels, susceptor position,and other parameters of a particular process. Of course, other computerprograms such as one stored on another memory device including, forexample, a floppy disk or another appropriate drive, may also be used tooperate system controller 150. An input/output device 156 such as a CRTmonitor and a keyboard is used to interface between a user and systemcontroller 150.

The process for smoothing a silicon surface in accordance with thepresent invention can be implemented using a computer program productwhich is stored in memory 152 and is executed by processor 154. Thecomputer program code can be written in any conventional computerreadable programming language, such as, 68000 assembly language, C, C++,Pascal, Fortran, or others. Suitable program code is entered into asingle file, or multiple files, using a conventional text editor, andstored or embodied in a computer usable medium, such as a memory systemof the computer. If the entered code text is in a high level language,the code is compiled, and the resultant compiler code is then linkedwith an object code of precompiled windows library routines. To executethe linked compiled object code, the system user invokes the objectcode, causing the computer system to load the code in memory, from whichthe CPU reads and executes the code to perform the tasks identified inthe program. Also stored in memory 152 are process parameters such asprocess gas flow rates (e.g., H₂ and HCl flow rates), processtemperatures and process pressure necessary to carry out the smoothingof silicon films in accordance with the present invention.

Experimental

A Epi process tuning tool was developed for growing doped and undopedsilicon (Si), doped and undoped silicon-germanium (SiGe), and/orgermanium (Ge) film on substrate wafers (e.g., a 300 mm substratewafer). The tool was developed from measuring the effects of processparameters including the ratio of heating lamp powers for differentheating zones on film uniformity. The experimental results were thenentered into a Microsoft Excel spreadsheet that plotted gain curvesshowing changes in film thickness as a function of the lamp powerratios. The Excel function “solver” was then used to calculate the lampratios that would achieve a target film thickness having highuniformity. The Epi process was then run with the calculated values ofthe power ratios to produce a SiGe film with excellent thicknessuniformity properties with one baseline wafer, and one tuning iteration.

The Epi growth process conditions for growing the baseline SiGe film aresummarized in Table 1: TABLE 1 Epi Process Conditions for GrowingBaseline SiGe Film Process Parameter Value Temperature 800° C. LowerPower Ratio 60% Upper Inner/Lower Power Ratio  50%/12.5% DCS Flow 100sccm GeH₄ (1%) Flow 200 sccm HCl Flow 150 sccm PH₃ (1%) Flow 250 sccmTime 150 sec Pressure 20 Torr H₂ Main 30 slm H₂ Slit 3 slm Accuset125/125

The process conditions for growing the baseline Epi film were set byintegration requirements, and to achieve desired electrical propertiesin the film. A DOE was performed to find values for the baseline processparameters to achieve a selective SiGe layer 300 Å thick, with a 16%germanium content, and a resistivity of 300Ω.

Experimental runs were then conducted with a 300 mm EPI Centuraepitaxial film growth system to determine the effects of processparameters on the film uniformity. In a series of DOEs, the processparameters were manipulated around the baseline conditions to measurethe effects on the uniformity of film properties such as thickness,resistivity, and germanium concentration. Because the iterative processrequired a lot of wafers, an attempt was made to find the most sensitiveparameters to effecting the uniformity of film properties.

Starting with the baseline process parameters, sensitivity experimentswere performed by making small deviations in each parameter, andobserving which parameters had the greatest effect on film uniformity.These experiments revealed the accusett for gas flow distribution, andlamp power adjustments had the greatest effect on film uniformity.Because the lamp power could be adjusted with greater resolution, thiswas the parameter used by the tuning tool to control film uniformity. Itwas also observed that film thickness uniformity was most representativeof uniformity of all the film properties measured, and this was the filmproperty to be controlled by the tuning tool.

The lamp power process parameter was defined by the distribution oflamps around various regions of a substrate that was rotatable on asusceptor in Epi process chamber. The lamps were divided into fourregions, called the 1) inner and 2) outer zones of the 3) upper and 4)lower modules. The power supplied to each region is independentlyadjustable. For a particular set of baseline process parameters, likepressure, gas-flows, and temperature set-point, the lamp powerdistribution factors for each region can be adjusted for radiation loss.Adjusting lamp power to maintain temperature consistency after changesin process parameters may be assisted by automated control processeslike those described in U.S. Pat. No. 6,164,816 to Aderhold et al,titled “TUNING A SUBSTRATE TEMPERATURE MEASUREMENT SYSTEM”, the entirecontents of which are hereby incorporated by reference for all purposes.

Measurements of thickness uniformity were made after small adjustmentsto lamp power in each of the regions. The effects were characterized bysubtracting the thickness-line-scan measured between the adjusted filmand a film formed with the baseline process parameters. The effect ofeach incremental unit change in the lamp power level on thicknessuniformity provided the data to determine a gain curve.

The thickness uniformity data was measured using a 46-point line scan ofthickness across the film. The 46-points were equally distributed acrosstwo perpendicular lines that intersected at the center of the 300 mmcircular substrate wafer. Gain curves were calculated for changes inthickness uniformity as a function of adjustments to the power suppliedto each lamp region. The parameters were considered independent, andeach parameter had an additive effect on the uniformity of the filmthickness. Gain curves plotting the effects of parameter adjustments onfilm thickness uniformity were entered into a Microsoft Excelspreadsheet, and used to predict a 46-point thickness distribution basedon the process parameter settings.

The parameters were calculated to produce a minimal standard deviationin the thickness uniformity using the Excel spreadsheet function“solver”. For small changes, the variation in the system is approximatedas linear, so linear extrapolation from an input measurement was used topredict the direction of a parameter change that will improve the filmthickness uniformity. Non-linear extrapolation models may also be usedfor predicting parameter settings that minimize variations in filmthickness.

The number of process parameters calculated by the tuning tool wasreduced from four to two by looking at the ratio of inner to outer zonelamp power ratio (first parameter), and the upper to lower lamp powerratio (second parameter). With the baseline film already made, threeadditional wafers were processed and film thicknesses measured. Wafer #1was run with the same parameters except a 2% higher inner to outer lamppower ratio, and wafer #2 ran with baseline parameters, except for a 2%higher upper to lower lamp power ratio. FIGS. 3A and 3B show changes inthe film thickness profiles caused by changes in each process parameter.

In FIG. 3A, a thickness profile is shown for a 2% increase from baselinein the ratio of lamp power between the inner and outer lamp zones. Thebaseline thickness data was subtracted from the wafer #1 thickness data,and normalized by division with 2%. To remove the slope in the dataacross the radius, a folding operation was used, and the data wassmoothed to get the line shown. In FIG. 3B, a thickness profile is shownfor a 2% increase in baseline in the ratio of lamp power between thelower and upper lamp modules. The baseline thickness data was subtractedfrom the wafer #2 thickness data, and also normalized by division with2%. A similar folding and smoothing operation was performed to get theline shown. Overall temperature sensitivity was measured at 5.6 Å/K. Thedata showing the effects of the two process parameters on the uniformityof film thickness were used to determine two gain curves, one for eachparameter.

The gain curves were incorporated into the tuning tool, and comparativeexperiments were run for tuning the two process parameters manually andwith the tool. FIG. 4 shows the thickness uniformity results from tuningthe process parameters. As shown, the thickness variation was 1.7% withan inner to outer power ratio of 52% (Wafer 303WB256), and 1.9% with aninner to outer ratio of 54% (Wafer 303WB259). In summary, with manualtuning the lowest variation in film thickness achieved was about 1.7%.The high thickness variation (i.e., low thickness uniformity) wasbelieved to be caused by interdependencies between lamp power settingsthat were not well understood. While changes the inner to outer lamppower ratio moved the thickness profile in a way predicted by the gaincurve (see FIG. 3A), it did not improve the overall smoothness of thefeature in the center of the wafer.

FIG. 5 shows the thickness uniformity results from tuning the processparameters with the aid of the Epi process tuning tool. The tuning toolfactors the interdependence of the lower to upper and inner to outerratios of lamp power when calculating the tuning values for both processparameters. The tuning tool output an increase in the upper to lowerlamp power ratio by 12%, while decreasing the inner to outer ratio by1%. The predicted thickness uniformity of 1.3% calculated by the toolmatched the actual thickness uniformity achieved in one run (wafer303WB362). This is down from 1.8% thickness uniformity for the waferproduced with the baseline starting parameters (Wafer 303WB350). Thus,compared with manual tuning, tuning process parameters with the help ofthe Epi process tuning tool shows significant improvements in thicknessuniformity after fewer tuning iterations.

Experiments can also be conducted to develop an effects profile to helpachieve target concentration distribution of a dopant. One targetprofile calls for a substantially uniform concentration of boron ofabout 1×10²⁰ atoms/cm² across a 300 Å thick SiGe epitaxial layer (Geconcentration of 20%). Measurements of the boron concentrationdistribution can be made after small adjustments to process parameterslike the flow rate of a diborane process gas. The measured boronconcentration distribution data can then be used to develop an effectsprofile that relates the effect of the diborane flow rate value to theconcentration distribution profile formed in the epitaxial layer. Theeffects profile may then be used to find values for the diborane flowrate that give the minimum deviation from a uniform concentrationdistribution profile of boron atoms in the epitaxial layer.

Having described several embodiments, it will be recognized by those ofskill in the art that various modifications, alternative constructions,and equivalents may be used without departing from the spirit of theinvention. Additionally, a number of well known processes and elementshave not been described in order to avoid unnecessarily obscuring thepresent invention. Accordingly, the above description should not betaken as limiting the scope of the invention.

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit unlessthe context clearly dictates otherwise, between the upper and lowerlimits of that range is also specifically disclosed. Each smaller rangebetween any stated value or intervening value in a stated range and anyother stated or intervening value in that stated range is encompassed.The upper and lower limits of these smaller ranges may independently beincluded or excluded in the range, and each range where either, neitheror both limits are included in the smaller ranges is also encompassedwithin the invention, subject to any specifically excluded limit in thestated range. Where the stated range includes one or both of the limits,ranges excluding either or both of those included limits are alsoincluded.

As used herein and in the appended claims, the singular forms “a”, “an”,and “the” include plural referents unless the context clearly dictatesotherwise. Thus, for example, reference to “a process” includes aplurality of such processes and reference to “the electrode” includesreference to one or more electrodes and equivalents thereof known tothose skilled in the art, and so forth.

Also, the words “comprise,” “comprising,” “include,” “including,” and“includes” when used in this specification and in the following claimsare intended to specify the presence of stated features, integers,components, or steps, but they do not preclude the presence or additionof one or more other features, integers, components, steps, acts, orgroups.

1. A substrate processing system comprising: a chamber; a substrate holder, located within the chamber, to hold a substrate; a precursor delivery system to introduce one or more precursors into the chamber; a heating system to heat the substrate; and a controller to control a process parameter in the precursor delivery system or the heating system; and a processor to calculate a value for the process parameter to achieve a substantially uniform epitaxial layer of a target thickness on the substrate, wherein the value is calculated using a gain curve derived from measurements of layer uniformity as a function of the value of the process parameter.
 2. The substrate processing system of claim 1, wherein the heating system comprises a plurality of lamps.
 3. The substrate processing system of claim 2, wherein the lamps are spatially distributed into a plurality of zones comprising an outer zone, an inner zone, a lower zone, and an upper zone.
 4. The substrate processing system of claim 3, wherein the process parameter comprises an inner zone to outer zone power ratio.
 5. The substrate processing system of claim 3, wherein the process parameter comprises a lower zone to upper zone power ratio.
 6. The substrate processing system of claim 1, wherein the epitaxial layer comprises a SiGe layer.
 7. The substrate processing system of claim 1, wherein the substrate is a 300 mm silicon wafer. 